The present invention relates to a method for designing and manufacturing a circulator module having a function of a directional coupler embedded therein.
Generally, a non-reciprocal circuit element such as a circulator and an isolator is a high-frequency communication part designed to allow a signal inputted through a predetermined port to be rotated in one direction in accordance with Faraday rotation so as to be transmitted to another port.
As shown in FIG. 1, in the case of the circulator, usually, three ports are provided and the signals having the same transfer coefficient and reflection coefficient are usually designed to be transmitted to other adjacent ports. Therefore, each port can be an input port and an output port for an adjacent port.
Generally, a circulator is located between a power amplifier and an antenna at a transmitting end of a wireless communication apparatus, so that a signal amplified from a power amplifier is transmitted to an antenna with a small loss. On the other hand, it serves to shield any signal so as to prevent a signal reflected from the antenna or unwanted signal from being transmitted to the power amplifier.
A directional coupler is a passive reciprocal network with four ports. It can sample one of the input signals for an input port while the other port has an electrical isolation property for the corresponding input signal. In order to ideally operate the directional coupler, all four ports should be matched and typically include a transmission line of a quarter wavelength. The directional coupler is used to sample a signal flowed in a certain direction.
FIG. 2 is a diagram illustrating a symbol of a general directional coupler.
As shown in FIG. 2, in the ideal directional coupler, the signal input to a port 1 (P1) is mostly transmitted to a port 2 (P2) and very small signal thereof is coupled at a port 3 (P3). However, it is not transmitted to a port 4 (P4). On the contrary, a signal input to the port 2 (P2) is sampled at the port 4 (P4). However, it is not transmitted to the port 3 (P3). That is, the directional coupler is an element designed to allow a signal flowed in a specific direction to be coupled only to a specific port.
FIG. 3 is a diagram illustrating a sampling signal transmission direction according to an input direction of a signal in a directional coupler.
As shown in FIG. 3, the directional coupler is generally constituted by connecting a termination resistor to one port. The signal input from a port 1 (P1) can be sampled at a port 3 (P3), while the coupling signal of the signal input to a port 2 (P2) is transmitted to a port to, which the termination resistor is connected, to be destroyed.
In the directional coupler, the amount of attenuation of the output signal (P2) with respect to the input signal (P1) is referred to as an insertion loss, the degree of insulation of the input signal (P1) at the port 4 (P4) is referred to as an isolation, the degree of coupling at the port 3 (P3) with respect to the input signal (P1) is referred to as coupling, and a value obtained by subtracting the coupling from the isolation is referred to as a directivity. Here, the directivity is a yardstick for evaluating how well the input signal from the port 1 (P1) is transmitted to the port 3 (P3) against the port 4 (P4) and is one of the most important evaluation items of the directional coupler.
The formula for this is as follows.[Equation]Insertion Loss(IL)=10*log(P1/P2)Isolation(I)=10*log(P1/P4)Coupling(C)=10*log(P1/P3)Directivity(D)=10*log(P3/P4)
Generally, directional coupler is located between power amplifier and antenna like a circulator and is used for sampling the magnitude of signal amplified from the power amplifier. As mentioned above, the directivity of the coupler is an important electrical characteristic because only the input signal amplified from the power amplifier should be sampled.
Since the demand for communication equipment increases and the price competition is fierce owing to the increase of the wireless communication demand and the development of the communication technology, the modularization of the used components is continuously required so as to reduce the insertion loss of the system, which is especially the electric characteristic of the communication equipment.
Accordingly, the researches on the modularization of the directional coupler and the circulator have been carried out. However, since each device is not only completely different in its electrical operation but also structurally made of completely different materials, there are many difficulties in modularization.
FIG. 4 is a circuit diagram in which the directional coupler and the circulator are modularized. The modules of the circulator and directional coupler implemented mostly in the prior art follow the configuration of the module shown in FIG. 4.
In some prior arts, the module is designed in such a manner that the directional coupler is implemented in a laminated substrate and the circulator is mounted on the laminated substrate. Such a module may cause the following problems. That is, since the heat generated in the circulator is transmitted to the bottom surface of the module through the laminated substrate, efficient heat transfer is difficult. Where the heat cannot be efficiently transferred, since the temperature of the circulator and the directional coupler in the laminated substrate is increased, the electrical characteristics of the module can be deteriorated. Also, the directional coupler and the circulator used in the base station and the repeater should withstand a high output signal. However, in case of the laminated substrate having the directional coupler, since a high frequency signal of high output is transmitted by a plurality of via holes, it cannot bear the high output signal. As a result, it is difficult to expect the ultimate improvement of the insertion loss through the module circuit, in that only the individual elements are collected in one place. In addition, in some prior arts mentioned above, the manufacturing cost is increased because it is manufactured by using an expensive substrate based on multilayered Teflon or an expensive LTCC substrate.